Bacillus thuringiensis (B.t.) produces an insect toxin designated as .delta.-endotoxin. It is synthesized by the B.t. sporulating cell. The toxin, upon being ingested in its crystalline form by susceptible insects, is transformed into biologically active moieties by the insect gut juice proteases. The primary target is insect cells of the gut epithelium, which are rapidly destroyed.
The reported activity spectrum of B.t. covers insect species within the order Lepidoptera, many of which are major pests in agriculture and forestry. The activity spectrum also includes the insect order Diptera, which includes mosquitos and black flies. See Couch, T. L. (1980) "Mosquito Pathogenicity of Bacillus thuringiensis var. israelensis," Developments in Industrial Microbiology 22:61-76; Beegle, C. C., (1978) "Use of Entomogenous Bacteria in Agroecosystems," Developments in Industrial Microbiology 20:97-104. Krieg, et al., Z. ang. Ent. (1983) 96:500-508, describe a B.t. isolate named Bacillus thuringiensis var. tenebrionis, which is reportedly active against two beetles in the order Coleoptera. These are the Colorado potato beetle, Leptinotarsa decemlineata, and Agelastica alni. In European Patent Application No. 0 202 739 there is disclosed a novel B.t. isolate active against Coleoptera. It is known as B. thuringiensis var. san diego (B.t.s.d.). U.S. Pat. No. 4,966,765 discloses the coleopteran-active Bacillus thuringiensis isolate B.t. PS86B1.
Cockroaches such as the German cockroach (Blatella germanica), Oriental cockroach (Blatta orientalis), American cockroach (Periplaneta americana) and Brown cockroach (Periplaneta americana) are some of the most important insect pests in homes and commercial structures. These pests have omnivorous feeding habits which result in the destruction of food, leather and fabrics. Cockroaches have also been implicated in the transmission of Salmonella and Toxoplasma. Cockroaches contain allergins. Approximately 7.5 percent of the human population is sensitive to these allergins.
Cockroaches are frequently controlled with baits. Because these baits are used in homes and restaurants, cockroach insecticides must be safe to humans. The heavy use of synthetic insecticides has resulted in the selection of resistant cockroach populations. New highly safe insecticides are necessary to control these resistant populations.